Trichomonads are protozoan parasites that infect humans and animals. There are over 15 species of Trichomonads. Trichomonas vaginalis (T. vaginalis) is a species of Trichomonad that humans and causes the condition trichomoniasis (or “trichomonosis” or “trich”) in both men and women. The parasite is sexually transmitted and is now the world's most common non-viral sexually transmitted disease (STD) agent. It is estimated that 5 to 8 million women acquire trichomoniasis annually in the United States, and up to 25% of sexually active woman are infected at any given time.
In men, trichomoniasis is estimated to account for 17% of non-chlamydial, non-gonococcal urethritis. The clinical symptoms vary tremendously among women, ranging from asymptomatic carriage to frank vaginitis; and the infection can persist indefinitely. Severe symptoms include abdominal pain with a foul-smelling discharge accompanied by irritation and discomfort similar to a vaginal yeast infection. Men tend to have more asymptomatic disease that lasts 4 months on average, but disease manifestations such as urethritis, prostatitis, balanoposthitis, and others have been documented in infected men.
In humans, infection with Trichomonas has severe health consequences. Trichomonas secretes proteinases that degrade vaginal antibodies, protective cell layers and immune response cells, thereby increasing the susceptibility of infected women to other sexually transmitted diseases. Studies have shown that women at risk for HIV have 2- to 10-fold greater risk of HIV infection if infected with T. vaginalis, and a male positive for both HIV and Trichomonas has 6 times more HIV in semen, thereby increasing the probability of infecting a partner (Wasserheit, 1992). Moreover, infection by Trichomonas increases the risk of acquiring cervical cancer, and can adversely affect both fertility and pregnancy (Yap et al., 1995; Zhang et al., 1995). Fortunately, if the infection by the parasite is successfully diagnosed, the patient can be treated in most cases.
The current diagnosis of trichomoniasis rests on the detection and morphologic identification of the live organism extracted from the vaginal cavity in women or the urethra in men. Identification is accomplished by microscopic examination of a saline wet mount preparation for the direct visualization of motile organisms. Although highly specific when positive, wet mounts are often negative in asymptomatic or mildly symptomatic patients and in women who have douched within the previous 24 hrs. Overall sensitivity or reliability of wet mount microscopy is 58% (Weise et al.), and can be as low as 30%. Wet mount microscopy can also be attempted from urine specimens following centrifugation to concentrate any trichomonads in the pellet, which is than resuspended and examined. Wet mount microscopy is highly inefficient when performed on urine samples, with sensitivity as low as 7% (compared to culture at 40%) (van Der Schee C., et al. J. Clin Microbiol. 1999 December: 37 (12) 4127-30). In addition, the wet mount microscopy method of detection, utilizing any of the sample types described, is subjective, tedious and time consuming, and requires a trained person.
Cultures of urogenital specimens may increase the number of detected cases. Unfortunately, the procedure requires several days to complete (typically 2-5 days) and must be conducted in special laboratories with trained personnel. Further, both of these methods require the parasites in the samples to be viable before they can be detected, constraining the suitability of certain sample types. For example, it has been determined that urine is not a suitable sample medium for culture-based diagnosis of Trichomonas, despite being more sensitive than wet mount (Mohamed et al. Sex. Transmitted Infect., 2001. 77(1) 78-9). Many attempts have been made to improve the diagnosis of Trichomonas from urine, as well as other sample types, using PCR. Although PCR is potentially more sensitive than wet mount or culture (87% according to the above reference), there is a lack of scientific consensus on what primer sequences are Trichomonas specific (PCR is not an FDA approved diagnostic method). Further, the problem of false positives in both discrepant samples and contaminated clinical sampleshinders the application of this technique. Highly amplified samples may provide a positive result that is not indicative of actual infection, but instead represents traces of a prior infection. In addition, PCR is a highly technical procedure with many manipulations and procedural controls, requires expensive equipment, and does not allow for point of care diagnosis; all factors mitigating against its suitability as a practical diagnostic method for Trichomonas.
A method for detecting Trichomonas infection by lysing the microorganisms in a sample and releasing their nucleic acids has been disclosed. The presence of Trichomonas is determined by hybridizing the released nucleic acids with probes. The method involves a large number of manipulations and the use of expensive detection equipment, and is less sensitive that wet mount microscopy.
The high frequency of Trichomonas infection, coupled with the likelihood of an adverse outcome for cases that are not treated expeditiously, makes clear the need for a rapid, sensitive, and accurate diagnostic test to detect Trichomonas infection and the ability to evaluate the effectiveness of the treatments. The diagnostic test should be suitable for use with a variety of samples suspected of containing Trichomonas, whether of not the sample contains live organisms, and in particular, should allow detection in a urine (for sampling men and women) and vaginal swap samples. In addition, the method should give high reliability, e.g., positive result for infected individuals.